1. Field of the Invention
The present invention relates generally to satellite global positioning systems (GPS), and more particularly, to an addressing device for restriction of receiving satellite television (TV) signal within an authorized location.
2. Description of the Related Art
Following development of broadband technology, multi-channel selected satellite video service enables more and more satellite TV subscribers day by day. Under the consideration of commercial benefit, a system provider usually limits the subscribers to conditionally receive digital TV signal (digital TV program) under authorization. Therefore, the Set-Top-Box (STB) has built therein with a processor for recognizing the authorization, which compares an authorization code carried in the satellite signal provided by the system end with the built-in code, and then outputs the digital TV signal (program) when the comparison is matched.
When a system provider owns more satellites, the provider can provide more different satellite TV channels for a variety of regions around the world; meanwhile, the provider serves different value added programs for the authorized subscribers of different regions and charges at different charging rates. In this way, an authorized subscriber also has to install a respective STB with a specific identification for accessing digital TV signal in each respective region, i.e. any region where satellite signal of the system provider is available. For example, U.S. Pat. Nos. 5,621,793, 6,009,116 & 6,108,365 each disclosed that a satellite TV receiving system, in which an outdoor satellite receiver can encrypt both of the satellite TV signal and the GPS addressing signal. The indoor STB of the subscriber needs to have a comparable GPS signal addressed at where the STB installs to match with the encrypted GPS addressing signal for enabling the subscriber to watch the digital TV of the respective zone. Therefore, the STB is an integrated circuit which can transmit and process both of the satellite TV and GPS signals, so the product of the STB costs a lot for making the circuit. In this way, while installing the digital TV system, the subscriber also needs to spend a lot doing so. Besides, the high-frequency GPS signal, transmitted straight by an GPS antenna integrated with the STB, is subject to attenuation within limited indoor space, so that the receiving quality of the GPS antenna of the indoor STB installed at the area having buildings of high density is vulnerable to be blocked by the buildings. For this reason, the integration of a GPS receiver with the indoor STB is unavoidable from GPS addressing error, even resulting in that the authorized subscriber is unable to receive the satellite channels due to the addressing error.
FIG. 4 illustrates a conventional satellite TV receiving system 1, which includes a satellite signal receiving device 11 capable of GPS addressing disclosed by the present inventor in the U.S. patent application Ser. No. 11/745,206. In light of this, the satellite TV system end can restrict a subscriber within a specific area receiving digital TV signal only by an STB connected to the satellite signal receiving device 11, and all of the subscribers in the same community only need to set one outdoor down-converter as the satellite signal receiving devices 11 and install the recognition program processed for GPS address recognition in the STB 12 of every subscriber. In this way, the indoor STB 12 of every subscriber does not need the high-cost GPS functionally integrated circuit, and the GPS signal processing circuit integrated inside the outdoor satellite signal receiving device 11 can decrease the GPS addressing error and then avoid missing the signal reception of the subscriber ends.
Because the outdoor satellite signal receiving device 11 is mounted to the focal center of a satellite dish 10, it needs to maintain a specific angle reflectively directing to a communication satellite for transmission of satellite signal. However, under the limitation of different bandwidth between the GPS communication and satellite TV transmission, it is difficult for the reception angle of the satellite dish 10 toward the satellite for GPS communication as well as toward that for the satellite TV transmission.
For these reasons mentioned all above, the conventional digital TV receiving system need improvement for optimal recognition of the GPS signal and reception of the satellite TV to ensure that the subscribers can accurately obtain high-quality satellite video services.